Preliminary Design of Small-Scale Supercritical CO2 Radial Inflow Turbines

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Tina Unglaube ◽  
Hsiao-Wei D. Chiang
Keyword(s):  
Optimum Design ◽  
Supercritical Co2 ◽  
Velocity Ratio ◽  
Design Procedure ◽  
Expansion Ratio ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Small Scale ◽  
Preliminary Design ◽  
Line Design

Abstract In recent years, supercritical CO2 (sCO2) Brayton cycles have drawn the attention of researchers due to their high cycle efficiencies, compact turbomachinery, and environmental friendliness. For small-scale cycles, radial inflow turbines (RIT) are the prevailing choice and one of the key components. A mean line design procedure for sCO2 RIT is developed and design space exploration conducted for a 100 kW-class turbine for a low-temperature waste-heat utilization sCO2 Brayton cycle. By varying the two design parameters, specific speed and velocity ratio, different turbine configurations are setup and compared numerically by means of computational fluid dynamics (CFD) simulations. Results are analyzed to conclude on optimum design parameters with regard to turbine efficiency and expansion ratio. Specific speeds between 0.2 and 0.5 are recommended for sCO2 RIT with small though flow (3 kg/s). The higher the velocity ratio, the bigger the turbine expansion ratio. Pairs of optimum design parameters that effectuate maximum efficiency are identified, with smaller velocity ratios prevailing for smaller specific speeds. The turbine simulation results for sCO2 are compared to well-established recommendations for the design of RIT from literature, such as the Balje diagram. It is concluded that for the design of sCO2 RITs, the same principles can be used as for those for air turbines. By achieving total-to-static stage and rotor efficiencies of 84% and 86%, respectively, the developed mean line design procedure has proven to be an effective and easily applicable tool for the preliminary design of small-scale sCO2 RIT.

Small Scale Supercritical CO2 Radial Inflow Turbine Meanline Design Considerations

2018 ◽  
Author(s):  
Tina Unglaube ◽  
Hsiao-Wei D. Chiang
Keyword(s):  
High Velocity ◽  
Gas Turbines ◽  
Velocity Ratio ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Working Fluid ◽  
Small Scale ◽  
Optimum Velocity ◽  
Set Up ◽  
Very High

In recent years closed loop supercritical carbon dioxide Brayton cycles have drawn the attention of many researchers as they are characterized by a higher theoretic efficiency and smaller turbomachinery size compared to the conventional steam Rankine cycle for power generation. Currently, first prototypes of this emerging technology are under development and thus small scale sCO2 turbomachinery needs to be developed. However, the design of sCO2 turbines faces several new challenges, such as the very high rotational speed and the high power density. Thus, the eligibility of well-established radial inflow gas turbine design principles has to be reviewed regarding their suitability for sCO2 turbines. Therefore, this work reviews different suggestion for optimum velocity ratios for gas turbines and aims to re-establish it for sCO2 turbines. A mean line design procedure is developed to obtain the geometric dimensions for small scale sCO2 radial inflow turbines. By varying the specific speed and the velocity ratio, different turbine configurations are set up. They are compared numerically by means of CFD analysis to conclude on optimum design parameters with regard to maximum total-to-static efficiency. Six sets of simulations with different specific speeds between 0.15 and 0.52 are set up. Higher specific speeds could not be analyzed, as they require very high rotational speeds (more than 140k RPM) for small scale sCO2 turbines (up to 150kWe). For each set of simulations, the velocity ratio that effectuates maximum efficiency is identified and compared to the optimum parameters recommended for radial inflow turbines using subcritical air as the working fluid. It is found that the values for optimum velocity ratios suggested by Rohlik (1968) are rather far away from the optimum values indicated by the conducted simulations. However, the optimum values suggested by Aungier (2005), although also established for subcritical gas turbines, show an approximate agreement with the simulation results for sCO2 turbines. Though, this agreement should be studied for a wider range of specific speeds and a finer resolution of velocity ratios. Furthermore, for high specific speeds in combination with high velocity ratios, the pressure drop of the designed turbines is too high, so that the outlet pressure is beyond the critical point. For low specific speeds in combination with low velocity ratios, the power output of the designed turbines becomes very small. Geometrically, turbines with low specific speeds and high velocity ratios are characterized by very small blade heights, turbines with high specific speeds and small velocity ratios by very small diameters.

scholarly journals Preliminary Design and Off-Design Analysis of a Radial Outflow Turbine for Organic Rankine Cycles

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 2118 ◽  
Author(s):  
Jun-Seong Kim ◽  
Do-Yeop Kim
Keyword(s):  
High Efficiency ◽  
Velocity Ratio ◽  
Design Procedure ◽  
Design Analysis ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Fine Tuning ◽  
Preliminary Design ◽  
Organic Rankine Cycles ◽  
Radial Outflow

Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The main purpose of this study is to provide more detailed information on the design methodology of the turbine. In this paper, a preliminary design program of a radial outflow turbine for organic Rankine cycles was developed. The program determines the main specifications of the turbine through iterative calculations using the enthalpy loss model and deviation angle model. For reliability evaluation of the developed algorithm, a 400.0 kW turbine for R143a was designed. The designed turbine was validated through computational fluid dynamics. As a result, the accuracy of the program was about 95% based on the turbine power, which shows that it is reliable. In addition, the turbine target performance could be achieved by fine-tuning the blade angle of the nozzle exit. In addition, performance evaluation of the turbine against off-design conditions was performed. Ranges of velocity ratio, loading coefficient, and flow coefficient that can expect high efficiency were proposed through the off-design analysis of the turbine.

Comparison of Partial vs Full Admission for Small Turbines at Low Specific Speeds

1985 ◽  
Author(s):  
Ennio Macchi ◽  
Giovanni Lozza
Keyword(s):  
Axial Flow ◽  
Design Procedure ◽  
Optimization Method ◽  
Expansion Ratio ◽  
Operating Conditions ◽  
Design Parameters ◽  
Basic Design ◽  
Partial Admission ◽  
Specific Speed ◽  
The One

Several methods are available for the optimization of basic design parameters and the preliminary efficiency prediction of axial flow turbine stages. However, their application is often questionable for stages having low specific speed and/or small volume flow rates. In particular, the question may arise whether a better performance is achieved by a partial admission, impulse stage or by a full admission reaction stage having lower blade height. The paper firstly reviews the available loss correlation methods applicable to partial admission turbines, then a comparison is performed between the efficiency achievable by partial and full admission stages designed for the same operating conditions. The turbine design procedure for both options is fully automatized by an efficiency optimization method similar to the one described in previous authors’ papers. The results of calculations are presented in the paper as a function of similarity parameters (specific speed, size parameter, expansion ratio). It is found that the results obtained with different correlations are relatively similar for “conventional” turbine stages (low expansion ratio, moderate size parameters), while important differences take place for very small sizes and/or in presence of important compressibility effects. The presented results can be useful: 1) to decide whether selecting full or partial admission solutions; 2) to optimize the degree of admission and the other basic design parameters, and 3) to predict with reasonable accuracy the stage efficiency.

Numerical Loss Investigation of a Small Scale, Low Specific Speed Supercritical CO2 Radial Inflow Turbine

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Joshua A. Keep ◽  
Ingo H. J. Jahn
Keyword(s):  
Supercritical Co2 ◽  
Cycle Performance ◽  
Small Scale ◽  
Preliminary Design ◽  
Baseline Design ◽  
High Loss ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Radial Inflow Turbine ◽  
Stage Efficiency

Radial inflow turbines, characterized by a low specific speed, are a candidate architecture for the supercritical CO2 Brayton cycle at small scale, i.e., less than 5 MW. Prior cycle studies have identified the importance of turbine efficiency to cycle performance; hence, well-designed turbines are key in realizing this new cycle. With operation at high Reynolds numbers, and small scales, the relative importance of loss mechanisms in supercritical CO2 turbines is not known. This paper presents a numerical loss investigation of a 300 kW low specific speed radial inflow turbine operating on supercritical CO2. A combination of steady-state and transient calculations is used to determine the source of loss within the turbine stage. Losses are compared with preliminary design approaches, and geometric variations to address high loss regions of stator and rotor are trialed. Analysis shows stage losses to be dominated by endwall viscous losses in the stator. These losses are more significant than predicted using gas turbine derived preliminary design methods. A reduction in stator–rotor interspace and modification of the blade profile showed a significant improvement in stage efficiency. An investigation into rotor blading shows favorable performance gains through the inclusion of splitter blades. Through these, and other modifications, a stage efficiency of 81% is possible, with an improvement of 7.5 points over the baseline design.

A preliminary multidisciplinary design procedure for tactical missiles

2018 ◽  
Vol 233 (9) ◽  
pp. 3445-3458 ◽  
Author(s):  
Mostafa Khalil ◽  
Anwer Hashish ◽  
Hamed M Abdalla
Keyword(s):  
System Development ◽  
Slenderness Ratio ◽  
Design Procedure ◽  
The Body ◽  
Multidisciplinary Design ◽  
Design Parameters ◽  
Preliminary Design ◽  
Empirical Formulas ◽  
Detail Design ◽  
The Impact

During missile system development, multidisciplinary design procedure is iteratively implemented based on the missile objective and target nature including internal ballistic, warhead function, and airframe configuration. By applying missile preliminary design, a good estimation for different design parameters can be obtained which will be useful through further detail design process. The aim of this paper is to build a preliminary design procedure for an unguided tactical missile that uses single-stage solid propellant motor to deliver a defined payload mass to a desired ground range. Based on data of available similar mature missile systems, two empirical formulas are developed to serve in the initial sizing of the missile with consideration of slenderness ratio, warhead mass, and desired ground range. Two different design concepts are implemented for tubular and star grains with different propellant compositions and chamber filling coefficients while the body-alone airframe configuration is adopted. The results demonstrate the capability of the proposed design procedure in defining the detailed design parameters. The impact of changing the propellant compositions and chamber filling coefficients on the obtained ground range is also explored.

Supercritical CO2 Radial Turbine Design Performance as a Function of Turbine Size Parameters

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Jianhui Qi ◽  
Thomas Reddell ◽  
Kan Qin ◽  
Kamel Hooman ◽  
Ingo H. J. Jahn
Keyword(s):  
Supercritical Co2 ◽  
Design Space ◽  
Waste Heat ◽  
Small Scale ◽  
Scaling Effects ◽  
Radial Turbine ◽  
Improved Performance ◽  
Turbine Design ◽  
Line Design ◽  
Selection Of

Supercritical CO2 (sCO2) cycles are considered as a promising technology for next generation concentrated solar thermal, waste heat recovery, and nuclear applications. Particularly at small scale, where radial inflow turbines can be employed, using sCO2 results in both system advantages and simplifications of the turbine design, leading to improved performance and cost reductions. This paper aims to provide new insight toward the design of radial turbines for operation with sCO2 in the 100–200 kW range. The quasi-one-dimensional mean-line design code topgen is enhanced to explore and map the radial turbine design space. This mapping process over a state space defined by head and flow coefficients allows the selection of an optimum turbine design, while balancing performance and geometrical constraints. By considering three operating points with varying power levels and rotor speeds, the effect of these on feasible design space and performance is explored. This provides new insight toward the key geometric features and operational constraints that limit the design space as well as scaling effects. Finally, review of the loss break-down of the designs elucidates the importance of the respective loss mechanisms. Similarly, it allows the identification of design directions that lead to improved performance. Overall, this work has shown that turbine design with efficiencies in the range of 78–82% is possible in this power range and provides insight into the design space that allows the selection of optimum designs.

scholarly journals Design Criteria and Efficiency Prediction for Radial Inflow Turbines

1987 ◽  
Author(s):  
Antonio Perdichizzi ◽  
Giovanni Lozza
Keyword(s):  
Computer Code ◽  
Expansion Ratio ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Test Cases ◽  
Main Design ◽  
Turbine Efficiency ◽  
Design Variables ◽  
Specific Speed ◽  
Turbine Design

A theoretical investigation was performed to predict the maximum achievable efficiency of radial inflow turbines for different design conditions. The analytical tool used in the investigation is a computer code able to perform the contemporary optimization of the main design variables, in order to obtain maximum efficiency. Since the results are strictly dependent on the loss correlations, reliability of the efficiency predictions was tested at first by comparison with several test-cases available in literature: good agreement with experimental data was found, pointing to the validity of the results presented here. A large number of cases were analyzed: the efficiency and the main design parameters, obtained after the optimization process, are presented for optimum specific speed. Turbine efficiency was found to be dependent both on compressibility effects, related to the volume expansion ratio, and on actual turbine size, accounting for geometric non-similarity effects. Influence of non-optimum specific speed is also discussed. By means of similarity rules, the results enable turbine design to be performed in a simple way, for a variety of working fluids and design conditions.

A Design Method of Radial Fans Considering the Torque-Speed-Characteristic of the Motor

2010 ◽  
Author(s):  
Philipp Epple ◽  
Mihai Miclea ◽  
Klaus Pfannschmidt ◽  
Detlev Grobeis ◽  
Antonio Delgado
Keyword(s):  
High Speed ◽  
Design Method ◽  
Design Procedure ◽  
Design Stage ◽  
Maximum Efficiency ◽  
Cfd Analysis ◽  
Test Rig ◽  
Motor Design ◽  
Line Design ◽  
Speed Characteristic

The use of high speed radial impellers is very common in fans for industrial applications. The most common design case is the one with constant speed. In that case, one assigns the corresponding value to the speed n, hence the speed no longer matters in the further design procedure: it is given and it is constant. However, in many cases the speed is not constant, since it is governed by the torque-speed characteristic of the driving motor. In such a case it is necessary to consider the motor characteristic already at the design stage. In the present work a design method was developed in order to perfectly match the torque-speed characteristic of the radial impeller to the torque-speed characteristic of the driving motor. In such a way it is possible to design an impeller-motor unit with maximum efficiency. The extended impeller mean-line-design formulas presented in Epple [6] were complemented with the equations describing the motor torque-speed-characteristic. Both sets of equations where combined and solved in order to achieve a prescribed operating range at a maximum efficiency. In order to validate the design method, it was applied to an industrial fan which should be improved. That radial fan with spiral casing consisted of the main radial fan and a motor cooling axial fan at the other end of the shaft. This later fan was rotating at a too low speed leading to cooling problems of the motor. Hence, a new fan had to be designed which had to deliver the same hydraulic performance but at higher rotating speeds. This had to be done, however, on the given motor. That could only be done when properly designing an impeller matching its torque-speed characteristic to the torque-speed characteristic of the motor: it was an excellent task to validate the combined impeller-motor design procedure. Under these constrains six designs where performed and validated with a commercial CFD solver. The three best designs according to the CFD results were built as prototypes and measured at a standard test rig. The best design delivered the prescribed head-flow characteristic at an even improved hydraulic efficiency. The higher speed was also properly achieved. The design procedure is described and explained in detail and a detailed CFD analysis is presented, complemented by the experimental data obtained at the test rig. A final comparative analysis of the combined impeller-motor design method, the CFD analysis and the measurements is presented.

scholarly journals Mean-Line Design of a Supercritical CO2 Micro Axial Turbine

2020 ◽  
Vol 10 (15) ◽  
pp. 5069 ◽  
Author(s):  
Salma I. Salah ◽  
Mahmoud A. Khader ◽  
Martin T. White ◽  
Abdulnaser I. Sayma
Keyword(s):  
Waste Heat ◽  
Expansion Ratio ◽  
Design Tool ◽  
Single Stage ◽  
Flow Coefficient ◽  
Low Flow ◽  
Design Parameters ◽  
Axial Turbine ◽  
Inlet Conditions ◽  
Line Design

Supercritical carbon dioxide (sCO2) power cycles are promising candidates for concentrated-solar power and waste-heat recovery applications, having advantages of compact turbomachinery and high cycle efficiencies at heat-source temperature in the range of 400 to 800 ∘C. However, for distributed-scale systems (0.1–1.0 MW) the choice of turbomachinery type is unclear. Radial turbines are known to be an effective machine for micro-scale applications. Alternatively, feasible single-stage axial turbine designs could be achieved allowing for better heat transfer control and improved bearing life. Thus, the aim of this study is to investigate the design of a single-stage 100 kW sCO2 axial turbine through the identification of optimal turbine design parameters from both mechanical and aerodynamic performance perspectives. For this purpose, a preliminary design tool has been developed and refined by accounting for passage losses using loss models that are widely used for the design of turbomachinery operating with fluids such as air or steam. The designs were assessed for a turbine that runs at inlet conditions of 923 K, 170 bar, expansion ratio of 3 and shaft speeds of 150k, 200k and 250k RPM respectively. It was found that feasible single-stage designs could be achieved if the turbine is designed with a high loading coefficient and low flow coefficient. Moreover, a turbine with the lowest degree of reaction, over a specified range from 0 to 0.5, was found to achieve the highest efficiency and highest inlet rotor angles.

scholarly journals Preliminary Gas Turbine Combustor Design Using a Genetic Algorithm

1997 ◽  
Author(s):  
Arnaud Despierre ◽  
Peter J. Stuttaford ◽  
Philip A. Rubini
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Gas Turbine ◽  
Combustion Process ◽  
Design Procedure ◽  
Design Tool ◽  
Performance Criteria ◽  
Design Parameters ◽  
Transfer Model ◽  
Preliminary Design

A genetic algorithm, coupled with a versatile preliminary design tool, is employed to demonstrate the concept of an autonomous design procedure for gas turbine combustors with user specified performance criteria. The chosen preliminary design program utilises a network based approach which provides considerable geometric flexibility allowing for a wide variety of combustor types to be represented. The physical combustor is represented by a number of independent, though interconnected, semi-empirical sub-flows or elements. A full conjugate heat transfer model allows for convection, conduction and radiative heat transfer to be modelled and a constrained equilibrium calculation simulates the combustion process. The genetic algorithm, whose main advantage lies in its robustness, uses the network solver in order to progress towards the optimum design parameters defined by the user. The capabilities of the genetic program are demonstrated for some simple design requirements, for example zone fuel/air ratio, pressure drop and wall temperatures.

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